问题补充:
In the past,ice food.
A. used to keep
B. used to be used for keeping
C. was used to keeping
D. used to be used to keeping
答案:
A. used to keep
(答案→)B. used to be used for keeping
C. was used to keeping
D. used to be used to keeping
解析:考查情态动词的被动语态。句中used to be used for keeping中的used to是情态动词,意思是“过去常常”,而be used for 是动词use 的被动形式;这个句子还可以表达成:was used to keep 或used to be used to keep。